Questions   
Sort: 
 #2
avatar+9464 
+2

See

 

here:   https://web2.0calc.com/questions/help-plz_8828

 

and here:  https://web2.0calc.com/questions/please-help_50163

 

Confusedperson, if you use someone else's answer you need to give that person credit. If you find the answer somewhere else, please put a link to that source.

Jun 23, 2018
Jun 22, 2018
 #1
avatar+9464 
+2

4 sin2x   =   4 cos x  +  5

                                                   By the Pythagorean identity,   sin2x  =  1 - cos2x    so....

4( 1 - cos2x )   =   4 cos x  +  5

                                                   Distribute the  4  to the terms in parenthesees.

4  -  4 cos2x   =   4 cos x  +  5

                                                   Add   4 cos2 x   to both sides of the equation.

4   =   4 cos2x  +  4 cos x  +  5

                                                   Subtract  4  from both sides of the equation.

0   =   4 cos2x  +  4 cos x  +  1

                                                   Split   4 cos x   into two terms that we can use to factor by grouping.

 

0   =   4 cos2x  +  2 cos x  +  2 cos x  +  1

 

0   =   2 cos x ( 2 cos x  +  1 )  +  1( 2 cos x  +  1 )

 

0   =   ( 2 cos x  +  1 )( 2 cos x  +  1 )

 

0   =   ( 2 cos x  +  1 )2

                                      Take the square root of both sides.

0   =   2 cos x  +  1

                                      Subtract  1  from both sides.

-1   =   2 cos x

                                      Divide both sides by  2 .

-1/2   =   cos x

 

The angle that has a cosine of   -1/2   in the interval  [0, pi)   is   2 pi / 3

 

x  =  2 pi / 3

Jun 22, 2018

4 Online Users

avatar